Better solution to the IN-list issue: instead of having an arbitrary cutoff,

treat Var and non-Var IN-list items differently.  Only non-Var items are
candidates to go into an ANY(ARRAY) construct --- we put all Vars as separate
OR conditions on the grounds that that leaves more scope for optimization.
Per suggestion from Robert Haas.

diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index ced222578db86251b5fd08cf8e1543be1d89f160..b5299d010a617ac75e3295ba64d485ea9743a3fc 100644 (file)
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.236 2008/10/25 17:19:09 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.237 2008/10/26 02:46:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -939,11 +939,13 @@ transformAExprOf(ParseState *pstate, A_Expr *a)
 static Node *
 transformAExprIn(ParseState *pstate, A_Expr *a)
 {
+       Node       *result = NULL;
        Node       *lexpr;
        List       *rexprs;
+       List       *rvars;
+       List       *rnonvars;
        bool            useOr;
        bool            haveRowExpr;
-       Node       *result;
        ListCell   *l;
 
        /*
@@ -959,41 +961,33 @@ transformAExprIn(ParseState *pstate, A_Expr *a)
         * possible if the inputs are all scalars (no RowExprs) and there is a
         * suitable array type available.  If not, we fall back to a boolean
         * condition tree with multiple copies of the lefthand expression.
+        * Also, any IN-list items that contain Vars are handled as separate
+        * boolean conditions, because that gives the planner more scope for
+        * optimization on such clauses.
         *
         * First step: transform all the inputs, and detect whether any are
-        * RowExprs.
+        * RowExprs or contain Vars.
         */
        lexpr = transformExpr(pstate, a->lexpr);
        haveRowExpr = (lexpr && IsA(lexpr, RowExpr));
-       rexprs = NIL;
+       rexprs = rvars = rnonvars = NIL;
        foreach(l, (List *) a->rexpr)
        {
                Node       *rexpr = transformExpr(pstate, lfirst(l));
 
                haveRowExpr |= (rexpr && IsA(rexpr, RowExpr));
                rexprs = lappend(rexprs, rexpr);
+               if (contain_vars_of_level(rexpr, 0))
+                       rvars = lappend(rvars, rexpr);
+               else
+                       rnonvars = lappend(rnonvars, rexpr);
        }
 
        /*
-        * We prefer a boolean tree to ScalarArrayOpExpr if any of these are true:
-        *
-        * 1. We have a RowExpr anywhere.
-        *
-        * 2. There's only one righthand expression --- best to just generate a
-        * simple = comparison.
-        *
-        * 3. There's a reasonably small number of righthand expressions and
-        * they contain any Vars.  This is a heuristic to support cases like
-        * WHERE '555-1212' IN (tab.home_phone, tab.work_phone), which can be
-        * optimized into an OR of indexscans on different indexes so long as
-        * it's left as an OR tree.  (It'd be better to leave this decision
-        * to the planner, no doubt, but the amount of code required to reformat
-        * the expression later on seems out of proportion to the benefit.)
+        * ScalarArrayOpExpr is only going to be useful if there's more than
+        * one non-Var righthand item.  Also, it won't work for RowExprs.
         */
-       if (!(haveRowExpr ||
-                 list_length(rexprs) == 1 ||
-                 (list_length(rexprs) <= 32 &&
-                  contain_vars_of_level((Node *) rexprs, 0))))
+       if (!haveRowExpr && list_length(rnonvars) > 1)
        {
                List       *allexprs;
                Oid                     scalar_type;
@@ -1004,9 +998,9 @@ transformAExprIn(ParseState *pstate, A_Expr *a)
                 * since the LHS' type is first in the list, it will be preferred when
                 * there is doubt (eg, when all the RHS items are unknown literals).
                 *
-                * Note: use list_concat here not lcons, to avoid damaging rexprs.
+                * Note: use list_concat here not lcons, to avoid damaging rnonvars.
                 */
-               allexprs = list_concat(list_make1(lexpr), rexprs);
+               allexprs = list_concat(list_make1(lexpr), rnonvars);
                scalar_type = select_common_type(pstate, allexprs, NULL, NULL);
 
                /* Do we have an array type to use? */
@@ -1017,14 +1011,14 @@ transformAExprIn(ParseState *pstate, A_Expr *a)
                if (array_type != InvalidOid)
                {
                        /*
-                        * OK: coerce all the right-hand inputs to the common type and
-                        * build an ArrayExpr for them.
+                        * OK: coerce all the right-hand non-Var inputs to the common type
+                        * and build an ArrayExpr for them.
                         */
                        List       *aexprs;
                        ArrayExpr  *newa;
 
                        aexprs = NIL;
-                       foreach(l, rexprs)
+                       foreach(l, rnonvars)
                        {
                                Node       *rexpr = (Node *) lfirst(l);
 
@@ -1040,19 +1034,21 @@ transformAExprIn(ParseState *pstate, A_Expr *a)
                        newa->multidims = false;
                        newa->location = -1;
 
-                       return (Node *) make_scalar_array_op(pstate,
-                                                                                                a->name,
-                                                                                                useOr,
-                                                                                                lexpr,
-                                                                                                (Node *) newa,
-                                                                                                a->location);
+                       result = (Node *) make_scalar_array_op(pstate,
+                                                                                                  a->name,
+                                                                                                  useOr,
+                                                                                                  lexpr,
+                                                                                                  (Node *) newa,
+                                                                                                  a->location);
+
+                       /* Consider only the Vars (if any) in the loop below */
+                       rexprs = rvars;
                }
        }
 
        /*
         * Must do it the hard way, ie, with a boolean expression tree.
         */
-       result = NULL;
        foreach(l, rexprs)
        {
                Node       *rexpr = (Node *) lfirst(l);